Add rudementary test for MDNFilter

Author: psomhorst

tests/test_mdn_filter.py

@@ -0,0 +1,35 @@
+import numpy as np
+import scipy as sp
+
+from eitprocessing.filters.mdn import MDNFilter
+
+SAMPLE_FREQUENCY = 20
+MINUTE = 60
+
+
+def test_mdn_working():
+    n_samples = 10000
+    heart_rate = 70 / MINUTE
+    respiratory_rate = 12 / MINUTE
+
+    signal = np.random.normal(2.0, 1.0, n_samples)
+
+    mdn_filter = MDNFilter(sample_frequency=SAMPLE_FREQUENCY, heart_rate=heart_rate, respiratory_rate=respiratory_rate)
+    filtered_signal = mdn_filter.apply_filter(signal)
+
+    f, Pxx = sp.signal.welch(signal, fs=SAMPLE_FREQUENCY)
+    filtered_f, filtered_Pxx = sp.signal.welch(filtered_signal, fs=SAMPLE_FREQUENCY)
+
+    current_frequency_center = heart_rate
+    while current_frequency_center < mdn_filter.noise_frequency_limit:
+        notch_distance = mdn_filter.notch_distance
+        frequency_band = (f > current_frequency_center - notch_distance) & (
+            f < current_frequency_center + notch_distance
+        )
+        mean_power = np.mean(Pxx[frequency_band])
+
+        filtered_mean_power = np.mean(filtered_Pxx[frequency_band])
+
+        assert filtered_mean_power < mean_power
+
+        current_frequency_center += heart_rate